Box 8A Tundra and taiga Northern taiga, Hovfjallet, central Sweden Source: redrawn from J Meeus Located in the arctic and boreal zones, these landscapes resemble potential natural conditions. The fragile ecosystems of the arctic tundra are vulnerable to physical impacts which can produce irreversible changes; protection of these areas is therefore much warranted. The tundra and taiga are sparsely vegetated and open. Permafrost, low temperatures and water shortages make the vegetation period short and intense. While boreal swamps have been much drained during the last century, the subtaiga is a semi-open landscape with a combination of arable crops and forests. The northern taiga is illustrated in further detail below. Northern taiga The northern taiga is a semi-open coniferous forest in the hills and plains of the Nordic and the northern Russian region. The thickest forests are to be found in the river valleys and on the river terraces. The dominant trees are spruce, pine and birch, which give the northern taiga its appearance of uniformity and homogeneity (National Atlas of Sweden, 1990­92; Anon, 1988). Lichens, mosses and berry-bearing shrubs cover the ground in between a fine-meshed network of forest roads. Severe frost makes the growing season short (no more than 100 days), while the mean annual temperature is low (+1° C). There is an excess of water during the year, but because of a low water-retaining capacity of the sandy podzols, there can be severe drought problems during the growing season. Only some small-scale forestry and extensive grazing is possible. In the Nordic regions, forest fires are successfully controlled. The forest trees are cut mainly to provide the local population with wood. Reindeer pastures can be found as well. In Finland and Sweden in particular, many old wooded pastures and extensively used stands of birch and other deciduous trees have had to make way for conifer plantations (Bernes, 1993). Currently, the northern margin of the northern taiga is receding in a southerly direction, a shift which is being accompanied by an advance of the tundra. While this is most probably due to the establishment of industrial settlements and the construction of roads and railways (Symons, 1990), climatic changes might be another contributing factor.